The present embodiments relate to automated spectral fat saturation.
Magnetic resonance tomography (MRT) is an imaging method that is used primarily in medical diagnostics. MRT uses a high and homogeneous static magnetic field (e.g., the B0 field). With MRT, the relaxation times of nuclear spins in response to a high-frequency (HF) excitation pulse are observed (e.g., the longitudinal relaxation time T1 and the transverse relaxation time T2). In this process, the measurement of relaxation times of the hydrogen nucleus (i.e., a proton) is important due to prevalence in the human body. One challenge with MRT is to produce a clear contrast between fat tissue and aqueous tissue and, for example, to minimize disruptive influences of fat signals in aqueous tissue. Fat and water molecule signals may be separated due to the different chemical shift of both signals. Chemical shift refers to a shift of the resonant frequency of a nucleus as a function of the electrical and chemical environment. One method for suppressing fat signals based on the different chemical shift of hydrogen nuclei in fat tissue and aqueous tissue is known as spectral fat saturation. In a magnetic resonance (MR) spectrum, the resonances of hydrogen nuclei in fat and water molecules are manifested as separate signals in the form of a fat and water peak. A spectrally selective HF excitation pulse is then emitted, which only excites the hydrogen nuclei in the fat tissue so that longitudinal magnetization in the fat is converted to transverse magnetization. This is dephased immediately by a magnetic field gradient, so that the fat tissue may no longer be shown by the imaging sequence that directly follows. Spectral fat saturation is, however, susceptible to inhomogeneities of the B0 field and the respective transverse relaxation times within the measurement volume, because these determine the position and width of the fat peak in the MR spectrum. This dependency therefore provides that the quality of fat signal suppression may be spatially distributed in an inhomogeneous manner. One possible way of adjusting the homogeneity of the B0 field is referred to as shimming. Therefore, most MRT systems have shim coils that are able to correct even more complex spatial magnetic field patterns.
DE 10 2009 018 878 B4 discloses a method for imaging in magnetic resonance tomography using spectral fat saturation or spectral water excitation in a tissue region to be imaged of a patient to be examined. The method includes frequency adjustment measurement of a region of a patient to be displayed using a selected first coil section of the MRT system, and exact determination of the resonant frequency of water based on the spectrum obtained in the frequency adjustment measurement and including the resonant frequencies of fat and water. The method also includes repeating the frequency adjustment measurement and the determination using at least one further selected second coil section of the MRT system adjacent to the first coil section. The method includes measuring a k space dataset using a coil section or a coil section combination based on the water resonant frequency assigned to the coil sections. The method also includes repeating the measuring of the k space with other coil sections or other coil section combinations until the entire tissue region to be displayed has been measured. The method includes combining the measurement results obtained in the measuring of the k space and the repeating of the measuring, and displaying the result obtained in the combining in the image space in the form of an overall image of the tissue region to be displayed.